1. Field of the Invention
The present invention may relate generally to memory apparatus for use in a data processing system and particularly to open loop control of stepper motor drive of rigid disc memory apparatus having special mechanical control and cooling features.
2. Description of Prior Art
In the prior art, rigid magnetic discs for use with data processing systems as digital information memory devices have generally been driven by motors under servomechanism or closed-loop control. These motors, which were used for positioning the apparatus that supports the magnetic heads for writing information onto and reading information from the disk, were usually linear (voice-coil) type motors. Rotary type motors may have been used, but if so, they were not stepping (or stepper) motors as far as is known.
But, stepping motors had been used with non-rigid, or "floppy," or flexible disc media, as for example, disclosed in U.S. Pat. No. 4,071,866 which discloses a lead-screw arrangement for coupling step rotation of the stepping motor to apparatus which supports the magnetic heads. Floppy discs are less expensive than rigid discs, but they have shortcomings which include relatively poor reliability and short life, since the magnetic heads are in contact with the surface of the floppy discs! By contrast, rigid magnetic discs do not contact the magnetic heads which "fly" on an air bearing relative to the disc surface.
Another problem associated with floppy discs is that they cannot store nearly as much binary information as can a rigid disc. One reason for this limited capacity is that floppy discs usually have a substantially lower track density (density of concentric rings or tracks which can be allocated as concentric areas on the surface of this disc to retain binary information) than do the rigid magnetic discs. While this is a disadvantage of floppy discs, a concomitant advantage of floppy discs is that because of its lower track density, its magnetic head actuator is sufficiently accurate without closed-loop control. The avoidance of this extra closed-loop or servomechanism technology (mechanical, electronic, and electromechanical) provides a substantial reduction in cost, complexity, etc. On the other hand, although rigid magnetic discs can store substantially more binary information than floppy discs, since track density in rigid discs can be much greater, actuators of rigid disc magnetic heads ususally required closed loop and servomechanism control with its accompanying higher cost, complexity, etc.
However, there have been designs in the prior art which have approached but not achieved an open-loop system for rigid discs. In the early 1960's, IBM developed a rigid disc system which employed a d.c. motor and a mechanical, ratchet-type, detent control. There was feedback involved, although the type of control may not be necessarily characterized as closed-loop control. It suffered from low track density capacity, mechanical wear, poor reliability, and other problems.
This older technology employed "straddle-erase" magnetic heads, which were used to provide clear separation between concentric magnetic rings of binary information, by using erase heads on both sides of (in the radial direction, and thus straddling) the read/write head. This "gap-insurance" was necessary in the older technology since head position control (and possibly even with servocontrol) was not that good.
Straddle erase heads are not readily available today in "Winchester" technology (a lubricated, rigid magnetic disc, with lightly loaded heads in a sealed environment), which the present invention employs. Although the present invention uses open loop control with high track density discs, it is still sufficiently advanced in its control design to avoid need for straddle erase heads (which, as noted, are not readily available anyway).
A substantial advance in the technology of computer disc memories has been achieved by the present invention. Higher reliability and greater storage capacity characteristics of rigid magnetic discs are now combined with the lower cost and less complex characteristics of an open loop disc drive. The present invention, which is operating successfully, thus combines the best of both "worlds" and is therefore a solution to these above-noted shortcomings of the prior art.
In the prior art, there is a mechanical control extending outward from the Winchester technology sealed enclosure permitting the locking of the magnetic heads upon the "landing zone" position of the disc, an uncritical area where information is not intended to be stored. Zero alignment normally takes place at the factory, and was usually accomplished by separate control. The present invention provides a convenient improvement to this zeroing procedure by permitting the same "landing zone" lock to function in the same position as a zeroing control which provides a zero track reference, and in another position establishes a safety travel-limit for movement of the magnetic head support arm during operation of the disc drive.
Other prior art frustrations related to precise adjustments of the heads above and below the surface of this disc, since, as noted, magnetic heads during operation or spinning of the disc fly on an air bearing developed by relative motion of heads and ambient air. In the past, precision machining of the multiple pieced supporting structure was required to provide the precise (about 0.02 inches) tolerance required. The present invention provides a solution to this prior art precision machining problem by employing shim or spacer apparatus to permit adjustment of heads relative to disk surface.
Another prior art concern related to mis-alignment or erroneous orientation of sensing transducers such as an optical transducer employed in the memory apparatus when the memory apparatus was being fabricated. In the optical transducer situation, the spinning magnetic disc structure could include an optical mask spinning therewith, and with a toothed or apertured periphery for purposes of permitting and preventing optical communication in the coupled optical transducer. The transducer counts the teeth and thereby generates information indicative of angular speed and displacement of the spinning shaft. In certain prior art memory apparatus constructions, alignment of optical heads with the optical mask and potential damage to them was a critical problem because of the high density of mechanical parts in close proximity to the location in which the optical transducer would be positioned. Accordingly, the present invention is a solution to this problem of the prior art by providing special keying means for allowing only the unique and proper insertion, mounting, and orientation of the optical transducer.
Yet another problem of the prior art, and a problem which is associated not only with this memory technology, but with virtually all electro-mechanical apparatus, is the removal of heat which has been generated by operation of the electrical and mechanical components of the apparatus. Normally, a separate mechanism such as a separate fan is included somewhere within the housing of the apparatus to create a draft or flow of air which provides the necessary heat transfer and stabilization of temperatures within the apparatus housing. But, this additional fan requires additional space, additional cost, additional power, and generates additional heat which is the precise problem it is trying to compensate. Accordingly, the present invention is an improvement in this area of temperature control by making use of rotary or pivotable motion already present for other purposes and synergistically providing a cooling effect without addition of separately powered fan apparatus.
The foregoing and other problems of the prior art are attended to by solutions described and embodied herein, as will be elaborated on hereinbelow.